Thermoplastic polyester resins such as polybutylene terephthalate and polyethylene terephthalate exhibit excellent mechanical strength, chemical resistance, electrical insulating properties, and the like, and also exhibit excellent heat resistance, moldability and recyclability, and are therefore widely used in components for electrical and electronic equipment, and components for motor vehicles, and also in electrical equipment components, mechanical components, and the like.
The spread of multifunctional portable terminals such as smartphones has been rapid in recent years, and thermoplastic polyester resins are widely used in components thereof. Because multifunctional portable terminals have been improved significantly in the function and in the performance and reduced in the weight, size and thickness, antennas required for portable terminals are formed as circuits inside portable terminals. Antenna circuits are formed as electrically conductive metal circuit patterns, but the insides of portable terminals and the like are shaped narrow and complicated, and in cases where antenna circuits are formed in such places, circuit patterns are three-dimensional patterns.
In order to form a circuit pattern on the surface of a resin product that is not electrically conductive, one method is to use ordinary electroless plating, in which a surface of a molded article is etched with an acid, a catalyst is applied and used as a catalyst for subsequent electroless plating (chemical plating), the molded article is immersed in an electroless plating liquid so as to form an electrically conductive layer, and a variety of metals are then plated so as to form a circuit pattern. This method has the drawback of requiring a complex process involving acid treatment, neutralization treatment, catalyst formation and catalyst activation.
A method that has attracted a great deal of interest in recent years is a method known as laser direct structuring (hereinafter also referred to as LDS). In this method, a surface of a molded article comprising a resin material containing a metal compound is irradiated with a laser in the shape of a circuit pattern, an activated metal layer is formed only on those regions of the surface of the molded article on which the circuit pattern is to be provided, thereby facilitating plating treatment, and plating is then carried out by means of electroless plating (or electroplating) using copper, nickel, gold, or the like, so as to construct a circuit pattern. Such LDS techniques are disclosed in PTL 1 to 3, for example.
However, even when LDS is applied to a thermoplastic polyester resin, there is a drawback that it is difficult for a plating to produce. This drawback is not ameliorated if the laser irradiation intensity is increased or decreased. In the invention disclosed in PTL 4, talc is blended in order to improve platability (see paragraph [0048]; Examples). However, this method has the problem that the mechanical properties (especially brittleness) of the product deteriorate.